1. Field of the Invention
The present invention relates to a background-picture compensating circuit using an on-screen display (hereinafter referred to as "OSD") signal. More particularly the invention relates to a background-picture compensating circuit using an OSD signal, wherein a window for an OSD character background picture is set around a predetermined portion of the OSD characters. The background picture level is made lower than the surrounding picture level by performing a half tone function without any separate half tone circuit therefor. An original picture is displayed covered by the background picture and the OSD characters.
2. Description of the Prior Art
The half tone function generally means that the luminance level around an OSD character becomes lower than that of an original picture signal to improve the OSD character display. Typically, the half tone is carried out by using an integrated circuit provided with the half tone function. This complicates the circuitry and increases its cost.
Japanese Laid-open Publication No. 61-269573 entitled "Half Tone Processing Circuit in a Television" discloses a technique whereby a half tone signal received during a blanking pulse output period of a character signal is supplied to a video signal processing circuit as a beam current limit signal for lowering luminance around the characters, so that the characters can easily be visually distinguished.
In other words, the prior art carries out the half tone function in such a manner that an automatic luminance limit circuit for providing the beam current limit signal to automatically control the luminance is supplied with the half tone signal during the blanking pulse output period of the character signal, and the half tone signal is then transmitted to the video signal processing circuit to thereby lower the luminance around the characters.
In the above construction, however, the luminance around the characters can be lowered by the half tone signal, but the half tone signal is supplied from an additional half tone circuit to thereby complicate the circuitry and increase cost.